The present invention relates to electronic modules, and more particularly, to wafer level modules and methods of fabrication therefor.
A typical conventional electronic module, such as a memory module, may include a plurality of packaged integrated circuit devices attached to a printed circuit board (PCB). The integrated circuit devices may be packaged in a number of different form factors, including traditional thru-hole packaging and surface mount (SMT) packaging conducive to manual and/or wave soldering techniques, as well as chip scale packaging (CSP) and wafer level chip scale packaging (WLCSP) that is configured for PCB attachment using solder ball techniques.
FIG. 1 shows a conventional module having WLCSP devices 50 mounted on a PCB 10. Though not shown in the drawing, the PCB 10 includes circuit traces that interconnect the devices 50 and passive devices 70, e.g., inductors, capacitors and resistors. The PCB 10 further includes edge connector contacts 12, which are configured to contact blades of an edge connector (not shown) that engages the edge of the PCB 10.
FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1. As shown, solder balls 57 connect the WLCSP devices 50 with the PCB 10. FIG. 3 shows an enlarged view of a portion of the WLCSP device 50, which includes a semiconductor substrate 51, a passivation layer 53, chip pads 52, a patterned redistribution layer 54, and a protective layer 55. The solder ball 57 contacts an exposed portion of the redistribution layer 54.
Conventional device packaging and interconnection technologies appear to be approaching a minimum feature size limit that may constrain designers' ability to further reduce the size of modules. Moreover, techniques that use soldered connections may present reliability and environmental problems. For example, for the module shown in FIGS. 1 and 2, mechanical shear stress on the solder balls induced by mismatch in thermal expansion coefficients of the device 50 and the PCB 10 may cause failure of the solder joint. In addition, the lead content of conventional solders can pose environmental issues.